Finding DC operating points at certain timepoints during TRANSIENT analysis

No, that doesn't make sense. The infotimes parameter does not cause spectre to compute a DC operating point at each of the specific time; instead it reports the operating point parameters for each device at that time. Essentially an operating point is the set of voltages and currents (for the nodes and branches) in the circuit, used as a starting point for many other analyses. In that context, removing the capacitors and inductors (setting them to 0) makes sense because you are trying to find the DC steady state solution. Then once the DC operating point has been found, we typically save the information about the operating point parameters for each device (often the parameters that are used in the small-signal models, like gm, gds etc).

With infotimes, this is during a transient. So all it is doing is saving the parameters for the devices at the bias point at that time. Removing the capacitors and inductors would be an odd thing to do, because then you'd essentially throw away all the storage elements in the circuit, and the operating point would be the same as the initial DC operating point (because it would have to find a consistent operating point in the absence of those devices - essentially finding the settled steady state again). So that's not what you'd want (I believe).

So unless the capacitor is discharged at that time anyway, I would expect the voltage across the capacitor to reflect what it actually is at that time in the transient. Anything else would be of little use, I think. Remember there are capacitors inside all the devices too - it's not just the physical capacitors that get set to 0 when a DC operating point is computed.

Hope that helps (and that I've not just rambled around in circles).

Regards,

Andrew.

No, that doesn't make sense. The infotimes parameter does not cause spectre to compute a DC operating point at each of the specific time; instead it reports the operating point parameters for each device at that time. Essentially an operating point is the set of voltages and currents (for the nodes and branches) in the circuit, used as a starting point for many other analyses. In that context, removing the capacitors and inductors (setting them to 0) makes sense because you are trying to find the DC steady state solution. Then once the DC operating point has been found, we typically save the information about the operating point parameters for each device (often the parameters that are used in the small-signal models, like gm, gds etc).

With infotimes, this is during a transient. So all it is doing is saving the parameters for the devices at the bias point at that time. Removing the capacitors and inductors would be an odd thing to do, because then you'd essentially throw away all the storage elements in the circuit, and the operating point would be the same as the initial DC operating point (because it would have to find a consistent operating point in the absence of those devices - essentially finding the settled steady state again). So that's not what you'd want (I believe).

So unless the capacitor is discharged at that time anyway, I would expect the voltage across the capacitor to reflect what it actually is at that time in the transient. Anything else would be of little use, I think. Remember there are capacitors inside all the devices too - it's not just the physical capacitors that get set to 0 when a DC operating point is computed.

Hope that helps (and that I've not just rambled around in circles).

Regards,

Andrew.